An opthalmological disorder, dry eye, is a common complaint of ophthalmic patients. Unaddressed conditions of dry eye can lead to erosion and abrasion of the epithelial cell surface of the cornea, raising susceptibility to infection. Progression of the disease can lead to ulceration of the cornea, even loss of sight.
A variety of irritants, injuries, and medical conditions predispose individuals to initiation of decreased lacrimal gland secretion resulting in deficient levels of aqueous tears protecting and nourishing the surface of the eye. There are environmental factors such as high altitudes, arid and windy climates, air pollution, desiccated air from central heat and central air conditioning, and exposure to cigarette smoke which can establish and/or enhance deterioration of the quantity and quality of tear production. Even extensive computer use can be a contributing factor as studies have shown significantly decreased blinking rates for users concentrating their attention on computer screens. Some advances in eye care, starting with the introduction of contact lenses, and currently, the popularity of the LASIK procedure for vision correction, have contributed to the recent growth of subject numbers with dry eye. Use of contact lenses results in absorption of tear film by the lens, with resultant physical irritation of the conjunctiva in the eyelids. LASIK can have a secondary effect of eye injury as nerves often can be severed or ablated during laser refractive surgery, which can lead to at least temporary dry eye syndrome of several months duration.
Disease and some physical conditions can predispose individuals to dry eye disorder, including; allergies, diabetes, lacrimal gland deficiency, lupus, Parkinson's disease, Sjogren's syndrome, rheumatoid arthritis, rosacea, and others. Medications for other diseases may cause or exacerbate dry eye disorders, including diuretics, antidepressants, allergy medications, birth control pills, decongestants and others.
Age related changes may induce or exacerbate dry eye as well. Post menopausal women experience changes in hormonal levels that can instigate or worsen dry eye, and thyroid imbalances may cause similar changes. Finally, aging itself can cause a reduction in lipid production with resultant dry eye.
Until recently, therapeutic interventions were limited to palliative measures to increase the moisture level of the eye. This is most frequently achieved with instillation of fluids which act as artificial tears. These fluids are often solutions which are instilled once or several times a day. For more severe cases of dry eye, artificial tear solutions which incorporate a thickener or ocular gels can enhance the amount of film retained on the eye. Alternatively, several night-time ointment therapies are available. The thickened solutions, gels, and ointments suffer from the limitation that vision can be impaired significantly upon application, rendering them less useful to the average subject who may require numerous applications during their waking, active hours. Another palliative intervention is the installation of temporary punctual occlusions, or even surgical closure of the normal drainage route of tears into the nasal cavity adjacent to the eye.
However, none of these interventions are effective in the treatment of this disorder. Hence, it is desirable to develop agents which effectively treat dry eye, preferably with minimal side effects.